Method and apparatus for providing uniform gas delivery to a reactor

ABSTRACT

A gas distribution system for a reactor having at least two distinct gas source orifice arrays displaced from one another along an axis defined by a gas flow direction from the gas source orifice arrays towards a work-piece deposition surface such that at least a lower one of the gas source orifice arrays is located between a higher one of the gas source orifice arrays and the work-piece deposition surface. Orifices in the higher one of the gas source orifice arrays may spaced an average of 0.2-0.8 times a distance between the higher one of the gas source orifice arrays and the work-piece deposition surface, while orifices in the lower one of the gas source orifice arrays may be spaced an average of 0.1-0.4 times a distance between the higher one of the gas source orifice arrays and the work-piece deposition surface.

FIELD OF THE INVENTION

The present invention relates to a gas distribution system for an atomiclayer deposition or chemical vapor deposition processing system in whicha vapor phase precursor is transported from an upstream source to areaction space above a substrate.

BACKGROUND

The chemical deposition of thin solid films from gaseous (vapor-phase)chemical precursors onto solid substrates is of great interest in manyareas including semiconductor fabrication, magnetic data storage,nanotechnology and others. In particular, atomic layer deposition (ALD)and chemical vapor deposition (CVD) processes are commonly used todeposit both dielectric and metal films onto semiconductor substrates.Increasingly, these applications require that the deposited film meetstrict standards for thickness uniformity across the substrate andrepeatability in such thicknesses over multiple substrates, while at thesame time the process equipment is required to provide high filmdeposition rates so as not to present a bottleneck in the overallfabrication process.

In order for CVD and ALD equipment to meet such requirements, the fluxof vapor precursors to the substrate must be tightly controlled andshaped. Often, there can be multiple gaseous precursors that must reactto form the desired film and all must be delivered to the substrate in aprecise and controllable manner. In some cases, it is advantageous tomix these multiple precursors together prior to introducing them intothe reactor chamber. In other cases, it is preferable to maintain theprecursors isolated from one another until they come into contact withthe substrate so as to prevent any unwanted premature reactions.

Generally, uniform precursor flow into the reaction chamber is attemptedby providing a flat plate with many small holes in between thegas-source and the substrate (a so-called showerhead). An earlydescription of a device for providing such axial-symmetric gas flowtowards a substrate is provided in U.S. Pat. No. 4,798,165 of deBoer etal. The diffusion plate or showerhead can have separate zones such thatsome holes are used for introducing one precursor and other holes areused for introducing the other precursor. In this way the precursors arekept separate so that no mixing occurs prior to the precursors enteringthe reaction space adjacent to the substrate.

One such showerhead is described in U.S. Published Patent Application2006-0021703 of Salvador P. Umotoy. In this design, the showerheadfaceplate has a number of gas passageways to provide a plurality ofgases to the process region without commingling of those gases. A gasdistribution manifold assembly is coupled so as to provide the differentgasses to the various gas holes in the faceplate.

Another design for maintaining gases in separate passageways until theyexit the distribution plate into the process region is described in U.S.Pat. No. 5,595,606. This showerhead includes a multiple block stack thatostensibly maintains two gases in separate passageways until they exitthe distribution plate into the process region.

While showerheads of the sort described above purport to maintainseparation of the various gases used in the ALD and CVD the presentinventors have observed that if the relative flow rates of the differentprecursors flowing through adjacent holes are not well designed,recirculation can occur along the showerhead faceplate between theholes. FIG. 1 illustrates this condition. Shown in the diagram is a cutaway view of a showerhead apparatus 10 having two individual gasmanifolds generally indicated at 12 and 14. The upper manifold 12includes gas passageways 16 a and 16 b, which provide means for the gasin manifold 12 to exit via holes 18 a and 18 b in the faceplate 20 ofshowerhead 10. Similarly, the lower manifold 14 includes gas passageways22 a and 22 b, which provide means for the gas in manifold 14 to exitvia holes 24 a and 24 b in faceplate 20.

As shown, recirculation of the different precursor gases has been knownto occur along the showerhead faceplate 20 between the holes associatedwith the different manifolds 12 and 14. This undesired mixing of theprecursors can cause unwanted reactions therebetween and reduce filmuniformity on substrates in proximity thereto. Furthermore, whenmultiple zones are present within a single showerhead the spacingbetween the outlet holes of different zones becomes constrained by thenumber and size of holes required for flow uniformity.

Another problem with such showerhead designs is that it is difficult orimpossible to maintain a difference in temperature between the twoprecursors because they both flow through the same solid plate 26 beforereaching the faceplate 20. In many cases, it would be desirable tomaintain precursors at different temperatures until they react at thesubstrate surface.

What is needed, therefore, is a gas distribution system that overcomesthese limitations of conventional showerheads.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a gas distributionsystem for a reactor having at least two distinct gas source orificearrays displaced from one another along an axis defined by a gas flowdirection from the gas source orifice arrays towards a work-piecedeposition surface such that at least a lower one of the gas sourceorifice arrays is located between an upper one of the gas source orificearrays and the work-piece deposition surface. The precise distance fromthe upper gas source orifice array (or the lower gas source orificearray) to the work-piece deposition surface depends on a number offactors, including the shape of the individual orifices in each of thearrays and the gas flow rates for each array. In general, the orificearrays are positioned within the reactor such that a relatively uniformdeposition over the work-piece surface can be achieved using thenecessary gases and flow rates for the particular layer to be deposited.In addition to the distance from the work-piece surface, the spacingbetween individual orifices of each array will affect the nature andquality of the deposited layer. Hence, orifices in the upper one of thegas source orifice arrays may spaced an average of 0.2-0.8 times adistance between the higher one of the gas source orifice arrays and thework-piece deposition surface, while orifices in the lower one of thegas source orifice arrays may be spaced an average of 0.1-2 times adistance between the higher one of the gas source orifice arrays and thework-piece deposition surface.

The higher one of the gas source orifice arrays may be a planarshowerhead having a generally uniform distribution of orifices acrossits faceplate. The lower one of the gas source orifice arrays mayinclude one or more conduits distributed axi-symetrically with respectto a radius of the planar showerhead. For example, the lower one of thegas source orifice arrays may include a number of spoke conduits leadingfrom an axially centered feed conduit, and each spoke conduit includinga number of individual orifices spaced an average of 0.1-2 times adistance between the higher one of the gas source orifice arrays and thework-piece deposition surface.

A further embodiment of the present invention provides for introducinggases into a reactor by flowing a purge gas from a first gas sourceorifice array disposed a first distance from a surface of a work-piecealong an axis defined by gas flow from the first gas source orificearray to the surface of the work-piece while flowing a first reactiveprecursor into the reactor from a second gas source orifice arrayseparate from the first gas source orifice array and disposed at asecond distance from the surface of a work-piece along the axis definedby gas flow, said second distance being between said first distance. Atan appropriate time, the flow of the first reactive precursor from thesecond gas source array may be stopped and the purge gas then flowedinto the reactor from one or more of the first gas source orifice arrayand the second gas source orifice array. When unused portions of thefirst reactive precursor have been evacuated from the reactor, a secondreactive precursor may be flowed into the reactor through the first gassource orifice array while flowing the purge gas into the reactorthrough the second gas source orifice array. Thereafter, the flow of thesecond reactive precursor from the first gas source array may bestopped, and unused portions of the second reactive precursor evacuatedwhile flowing the purge gas into the reactor from one or more of thefirst gas source orifice array and the second gas source orifice array.This cycle may be repeated as needed to form a film on a substratewithin the reactor.

Notwithstanding its applicability to ALD processes such as thosedescribed above, the invention is also useful in CVD and/or pulsed-CVDoperations as discussed further below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and notlimitation, in the figures of the accompanying drawings, in which:

FIG. 1 shows an example of undesired gas recirculation and mixing whichcan occur when a conventional showerhead having gas passageways withexit holes in a single plane is used;

FIG. 2 shows an example of a showerhead configured in accordance with anembodiment of the present invention so as to prevent or reduce suchundesired gas recirculation and mixing by displacing gas passageway exitholes into separate planes displaced from one another along an axisdefined by the gas injection axis;

FIG. 3 shows an example of a showerhead configured in accordance with anembodiment of the present invention in which a radial spoke gasinjection conduit is displaced beneath a planar gas distribution plate;and

FIG. 4 shows an example of an ALD reactor having with a gas distributionsystem configured in accordance with an embodiment of the presentinvention; and

FIG. 5 illustrates a variation of the ALD system shown in FIG. 4 inwhich multiple wafers are processed in a single rector.

DETAILED DESCRIPTION

Described herein are gas distribution systems for ALD, CVD and/or otherprocessing systems in which vapor phase precursors or other gases (e.g.,inert carrier gases) are transported from upstream sources to a reactionspace above a substrate. Unlike such distribution systems of the past,the present distribution systems are composed of two or more physicallyseparated gas source orifices. That is, embodiments of the presentinvention provide gas source orifices at different displacements from asurface of a substrate along an axis of the gas pathway from theorifices to that surface. Viewed differently, the gas source orifices(which may be supplied by a common manifold configured to provide gasesor precursors separately to each orifice) are separated from one anotheralong an axis defining a path for the gasses to travel between theorifices and the substrate.

Embodiments of the present invention provide both physical and thermalseparation of reactive precursors until they come into close proximityto the substrate. This not only avoids undesired reactions along thefaceplate of the showerhead, it also permits the individual precursorsto be delivered at their individual optimum temperatures. Furthermore,systems configured in accordance with the present invention providemanufacturers greater flexibility in designing gas flow manifolds foreach precursor, independent from the geometrical constraints of theother.

Turning now to FIG. 2, an example of a gas distribution system 28configured in accordance with an embodiment of the present invention isillustrated. Note that although this illustration depicts a gasdistribution system with two manifolds (or gas source orifice arrays asthey are sometimes termed herein), the present invention is not limitedto such systems. Any number of such manifolds can be used. In somecases, the gas distributions systems will have multiple gas orificesdisposed in a single plane (such as is the case for the systemillustrated in FIG. 1) and in addition will have other gas orificesdisposed in a different plane (as described below). In other cases,three or more such orifice arrays separately disposed from one anotheralong an axis of gas injection may be provided. Thus, the depiction of asystem employing two such arrays displaced from one another is meantonly to illustrate the concepts embodied in the present invention andshould not be viewed as limiting the scope of the invention to sucharrangements.

FIG. 2 then is a cut away view of a gas distribution system 28 havingtwo individual gas manifolds generally indicated at 30 and 32. The uppermanifold 30 includes gas passageways 34 a-34 d, which provide means forthe gas in manifold 30 to exit via holes 36 a-36 d in the faceplate 38of a distribution plate 40. The lower manifold 32 includes a generallycylindrical gas passageway 40, which provide means for the gas inmanifold 32 to exit via holes 44 a-44 c.

Of course, the individual manifolds are not limited to these illustratedconfigurations and, in general, any convenient configurations may beused to achieve desired gas distribution profiles within a reactionspace proximate to a substrate. Thus, planar, curved, corrugated,cylindrical or other manifolds/distribution devices may be employed. Forexample, the faceplate 38 of upper manifold 30 need not be a flat (orrelatively flat) surface as is shown in the illustration. Instead,faceplate 38 may have a corrugated or even saw tooth profile. Further,regardless of whether the faceplate 38 is flat or not, it need notnecessarily be planar. Instead, various embodiments of the presentinvention may find particular application for a curved (e.g., relativelyconcave or relatively convex) faceplate 38.

The lower manifold 32 may itself be something other than a cylindricalgas passageway. For example, the lower manifold may be a relativelyplanar diffuser plate. Alternatively, the lower manifold 32 may be aseries of radially projecting cylinders resembling the spokes of abicycle wheel (as is shown in later figures and described furtherbelow). In some cases the individual spoke-like orifice arrays may be ofdifferent lengths and/or diameters and arranged so as to provide adesired gas flow to a substrate. The spoke-like arrays may beindependent of one another or may be coupled to one another viaazimuthally-oriented or chord-like members and/or gas source orificearrays.

In some cases the distance between the lower manifold 32 and the uppermanifold 30 may be adjustable. For example, the lower manifold 32 may besuspended beneath the upper manifold 30 by one or more telescoping(e.g., pneumatic or hydraulic) supports which operate under the controlof a controller so as to set the lower manifold at a desired distancefrom the faceplate 38 of the upper manifold 30. Alternatively, thesupports or other means of adjusting the separation distance between themanifolds may be manually configurable. Different CVD and/or ALDprocesses may require such different spacings between the manifolds inorder to achieve desired deposition characteristics on substrates.

Whether adjustable or not, the optimal distance between the upper andlower manifolds may be dependent on the characteristics of theindividual orifices present therein. Hence, to accommodate a widevariety of applications, the present invention encompasses the use ofdifferent types of orifices in either or both of the manifolds. Someorifices may be substantially cylindrical in cross-section, while othersmay be more funnel-like in cross-section so as to provide a widerdispersal of the gas exiting the orifice than might otherwise beachieved using orifices having a cylindrical cross-section. So too maythe number of holes in each individual manifold be adjusted to provide adesired gas distribution profile at the surface of the work-pieceundergoing processing. Different arrangements of orifice types andnumbers in different radial areas of either or both of the manifolds mayprovide for relatively uniform deposition rates across an entire surfaceof a substrate. Individual orifices may be circular, rectangular,square, triangular, etc., in transverse section.

While these various arrangements of orifices of different types are notcritical to the present invention, the overall goal of providing a gasdelivery system configured to achieve substantially uniform depositionacross an entire substrate surface while avoiding undesired cross-mixingof precursor gases should not be overlooked. In the case of a lowermanifold having radial, spoke-like orifice arrays for gas distribution,reduced spacing between individual orifices would imply having morespokes in the entire array. This may not necessarily be desirable inthat a wider spacing with fewer individual orifices would provide feweropportunities for undesired mixing of precursor gasses along the arms ofthe lower gas distribution array and, hence, reduced overall formationof contaminant particles.

As shown in FIG. 2, manifold 32 is displaced from manifold 30 along anaxis (Z) in the direction of gas injection from the respective holes ofeach manifold. Hence, the recirculation of the different precursor gasesfrom the different manifolds does not lead to any undesired mixing ofthe precursors along the faceplate 38 of distribution plate 40. Thisimproves the film deposition characteristics of systems employing system28 over those which make use of conventional showerheads.

FIG. 3 shows an isometric view of the gas distribution system 28. Theupper manifold is composed of a relatively flat distribution plate 40with multiple through-holes 36 in faceplate 38 to allow precursor vaporsand purge gases to enter the reactor (not shown). The lower manifold 32is configured as an array of radial tubes 48 joined to a central inlet50. The tubes 48 have a series of outlet holes (not shown in detail inthis drawing) to provide for uniform delivery of precursor and purgegases. The tubes 48 may be organized as one or more conduits distributedaxi-symetrically with respect to a radius of the planar distributionplate 40.

FIG. 4 illustrates an example of an ALD reactor 52 having a gasdistribution system configured in accordance with an embodiment of thepresent invention. In this cut away view, a wafer 54 is placed on asusceptor 56 (which may be vertically movable along the Z axis and mayalso include a heater) beneath the gas distribution system 28. The gasdistribution system 28 may be part of a lid assembly for reactor 52 ormay be separate therefrom. As indicated above, the gas distributionsystem includes an upper manifold 30, which is configured to receiveprecursor A from an upstream source, and a lower manifold 32, which isconfigured to receive precursor B from a separate upstream source. Eachof the manifold may also be configured to receive purge gasses. Manifold30 distributes precursor A towards substrate 54 through holes (not shownin this view) in the faceplate 38, while manifold 32 distributesprecursor B towards substrate 54 through holes (also not shown in thisview) in radial arms 48. The radial arms are fed via central inlet 50.Manifold 32 is displaced below the faceplate 38 of manifold 30 along theaxis of gas injection towards the substrate 54 (the Z axis) by adistance “d”.

FIG. 5 illustrates a variation of the above-described system in whichmultiple wafers or other substrates 60 are accommodated in a singlereactor 52. The wafers 60 may be supported on a linear array 56′.Alternatively, the wafers may be placed in a radial array that resemblesa carousel. Accordingly, the wafers 60 could be aligned along radialdirections with respect to the center of a circular supporting element.A multi-wafer reactor of this type may be used where backsidedepositions can be tolerated (or otherwise compensated for) and mayimprove overall throughput. Similarly, reactors such as reactor 52 maybe configured for use in stand-alone tools or in multi-single wafertools or in cluster tools.

Importantly, the lower manifold 48 need not have a radial spokeconfiguration as depicted in the illustration. In some cases the lowermanifold may be a point source (i.e., a gas orifice having asubstantially circular or other cross-section). Alternatively, the lowermanifold 48 could be a planar (or relatively planar) source, a sourcehaving a concave cross-section, or a radial spoke configuration withspokes of varying lengths. Further, the lower manifold 48 may berelatively smaller or larger than as depicted in the illustration. Thatis, the lower manifold 48 may have a diameter equal to or greater thanthe substrate 54. or, the lower manifold may have a diameter smallerthan that of the substrate, as shown.

Moreover, precursor B need not necessarily be fed to the lower manifold32 via a single, central supply line. Instead, some configurations mayhave precursor B being fed to the orifice array through a lateral lineor other, non central axial-symmetric feed line or lines. The details ofsuch gas feed lines from an external gas supply source are not criticalto the present invention.

In one embodiment of the present invention, the faceplate 38 of manifold30 is located a distance “L” from the surface of substrate 54 on whichdeposition is to occur. In practice, “L” will be an average distance ofan intended plane defined by the faceplate 38 from the surface of thesubstrate 54 and individual distances of any point on the faceplate 38will reside at a distance L±δ1 from said surface, owing tononuniformities in the faceplate surface and the surface of thesubstrate 54. Preferably, the holes in faceplate 38 through whichprecursor A gases will be introduced to reactor 52 will spaced anaverage of 0.2-0.8 times L±δ1 from one another. In further embodiments,the holes in manifold 32 may be spaced an average of 0.1-2 times L±δ1from one another. Note that this latter spacing may be achieved throughselected positioning of the various radial arms 48 of manifold 32.

Further, the distance from the lower manifold 32 to the surface of thesubstrate 54 will be some fraction of L. In various embodiments of theinvention this distance may be 0.3-0.9 * L, and in one embodiment thatwas reduced to practice was 0.7L. Typically, L will be approximately oneinch.

During a typical ALD process in which the present gas distributionassembly would be used, manifold 30 will be flowing purge gas whilemanifold 32 is flowing reactive precursor B. In the next step of theprocess both manifolds 30 and 32 will flow purge gas to assist inremoving any unreacted precursor from the reactor 52. Unused precursorsand purge gases are exhausted from reactor 52 via a pumping arrangement(not shown). Next, precursor A will be introduced through manifold 30and purge gas will flow through manifold 32. Finally, both manifolds 30and 32 will flow purge gas to assist in removing any unreactedprecursor. The flows of precursor and purge gas may be alternated inthis fashion throughout the deposition process to allow the substrate 54to be sequentially exposed to each of the precursors without allowingthe precursors to mix in the gas phase.

The above-described process allows for uniform delivery of precursorvapor by introducing one of the reactant species through a flat platewith a plurality of through-holes while the second reactant species isintroduced through a set of conduits radiating outward from a centrallylocated inlet. The conduits are situated such that they are between theflat plate and the substrate. This provides delivery of both reactantswhile maintaining thermal and physical isolation between the chemicals.

In some ALD processes, one of the ALD half-reactions will be softsaturating while the other is not. In such cases it may be desirable tointroduce the precursor associated with the soft saturating halfreaction through the upper manifold. For example, the precursorassociated with the soft saturating reaction may require more uniformdistribution, as may be achieved through introduction via the upper,relatively planar gas orifice array. In contrast, the precursorassociated with the strongly saturating half-reaction in the ALD processmay be relatively insensitive to distribution via a nonuniform gasorifice array such as the lower manifold. This may not always be thecase, however, inasmuch as relative gas flow rates must also be takeninto consideration.

In addition to ALD processes, the present invention may be used inconnection with CVD and/or pulsed-CVD processes. In a typical CVDprocess both manifold 30 and manifold 32 may be flowing purge gasesand/or reactive precursors (potentially with respective carrier gasses).When a desired deposition has been achieved, the flow of reactiveprecursors will be stopped and either or both manifolds 30 and 32 mayflow purge gas to assist in removing any remaining precursors from thereactor 52.

In a pulsed-CVD process a first precursor and carrier gas may beintroduced continually through manifold 30 and the second precursorintroduced in a pulsed fashion through the lower manifold 32.Preferably, the precursor introduced via the lower manifold will be theone which has a dominant surface reaction during the CVD. As before,once the desired deposition has been achieved, the unused precursors andpurge gases are exhausted from reactor 52 while flowing purge gasthrough one or both of the manifolds.

In further embodiments, the two manifolds may be operated so as tovariously flow reactive precursors, precursors and carrier gases, and/orpurge gas at various times in an ALD, CVD or other process so as toachieve a desired deposition on a substrate within the reactor. Forexample, while a precursor is introduced via the upper manifold (with orwithout a carrier gas), the lower manifold may be used to introduce asecond precursor (with or without its own carrier gas) or purge gas andvice-versa.

Thus, a gas distribution system composed of distinct, physicallyseparated source orifices to supply precursor vapors and inert gases toa substrate has been described. The distinct gas sources are orientedsuch that one orifice is located between the substrate and the otherorifice. This prevents gas recirculation that is often observed withconventional showerheads, when the precursor vapors and inert gases areinjected through adjacent orifices, and prevents premature reactionsthat are often observed when the precursors and purge gases areintroduced through a single orifice. Stated differently, in contrast toconventional showerheads gas distribution systems configured inaccordance with the present invention do not provide a gas recirculationzone between the outlet orifices of the separate gas manifolds. Thisimproves purging and can minimize gas-phase mixing and turbulence, bothof which can lead to unwanted film deposition or particle formation

It should be apparent from the preceding discussion that the use ofseparate gas source orifices that are not constrained to a singleflat-plate allows much more freedom in designing the size and shape ofeach precursor manifold. When both precursor manifolds are constrainedto have their outlet orifices in the same horizontal plane as in aconventional showerhead, the designer may not be able to achieve optimalflow uniformity for both precursors. At a minimum, the designer may haveto resort to complex manifold and gas flow passages to achieve uniformflow. However, when separating the precursor manifolds into distinctorifices that are not in the same plane, in accordance with the presentinvention, it is much easier to obtain gas flow uniformity with simplegas flow passages. Of course, although the present invention wasdiscussed with reference to certain illustrated embodiments, theseexamples should not be used to limit the broader scope of the inventionas set forth in the following claims.

1. A gas distribution system for a reactor, comprising at least twodistinct gas source orifice arrays displaced from one another along anaxis defined by a gas flow direction from the gas source orifice arraystowards a work-piece deposition surface such that at least a lower oneof the gas source orifice arrays is located between a higher one of thegas source orifice arrays and the work-piece deposition surface.
 2. Thegas distribution system of claim 1, wherein orifices in the higher oneof the gas source orifice arrays are spaced an average of 0.2-0.8 timesa distance between the higher one of the gas source orifice arrays andthe work-piece deposition surface.
 3. The gas distribution system ofclaim 1, wherein orifices in the lower one of the gas source orificearrays are spaced an average of 0.1-2 times a distance between thehigher one of the gas source orifice arrays and the work-piecedeposition surface.
 4. The gas distribution system of claim 1, whereinthe higher one of the gas source orifice arrays comprises a planarsource.
 5. The gas distribution system of clam 4, wherein the planarsource comprises a showerhead.
 6. The gas distribution system of claim1, wherein the higher one of the gas source orifice arrays comprises agenerally uniform distribution of orifices across a faceplate.
 7. Thegas distribution system of claim 6 wherein the lower one of the gassource orifice arrays comprises one or more conduits distributedaxi-symetrically with respect to a radius of the planar showerhead. 8.The gas distribution system of claim 1 wherein the lower one of the gassource orifice arrays comprises one or more conduits distributedaxi-symetrically with respect to the higher one of the gas sourceorifice arrays.
 9. The gas distribution system as in claim 8, whereinthe lower one of the gas source orifice arrays comprises a number ofspoke conduits leading from an axially centered feed conduit, and eachspoke conduit includes a number of individual orifices spaced an averageof 0.1-2 times a distance between the higher one of the gas sourceorifice arrays and the work-piece deposition surface.
 10. A method forintroducing gases into a reactor, comprising flowing a purge gas intothe reactor from a first gas source orifice array disposed a firstdistance from a surface of a work-piece along an axis defined by gasflow from the first gas source orifice array to the surface of thework-piece while flowing a first reactive precursor into the reactorfrom a second gas source orifice array separate from the first gassource orifice array and disposed at a second distance from the surfaceof a work-piece along the axis defined by gas flow, said second distancebeing less than said first distance.
 11. The method of claim 10, furthercomprising stopping the flow of the first reactive precursor from thesecond gas source array.
 12. The method of claim 11, further comprisingflowing the purge gas into the reactor from one or more of the first gassource orifice array and the second gas source orifice array.
 13. Themethod of claim 11, further comprising flowing a second reactiveprecursor into the reactor through the first gas source orifice arraywhile flowing the purge gas into the reactor through the second gassource orifice array.
 14. The method of claim 13, further comprisingstopping the flow of the second reactive precursor from the first gassource array.
 15. The method of claim 14, further comprising flowing thepurge gas into the reactor from one or more of the first gas sourceorifice array and the second gas source orifice array.
 16. The method ofclaim 15, further comprising evacuating unused amounts of the secondreactive precursor from the reactor.
 17. The method of claim 11, furthercomprising evacuating unused amounts of the first reactive precursorfrom the reactor.
 18. A method for introducing gases into a reactor,comprising flowing a carrier gas and a reactive precursor into thereactor from a first gas source orifice array disposed a first distancefrom a surface of a work-piece along an axis defined by gas flow fromthe first gas source orifice array to the surface of the work-piecewhile flowing a second reactive precursor into the reactor from a secondgas source orifice array separate from the first gas source orificearray and disposed at a second distance from the surface of a work-piecealong the axis defined by gas flow, said second distance being less thansaid first distance.
 19. The method of claim 18, wherein the secondreactive precursor is flowed into the reactor in a pulsed fashion viathe second gas source orifice array.
 20. The method of claim 18, furthercomprising stopping the flow of reactive precursors into the reactorwhile flowing a purge gas into the reactor from one or both of the firstand second gas source orifice arrays.
 21. A method for introducing gasesinto a reactor, comprising flowing a first gas into the reactor from afirst gas source orifice array disposed a first distance from a surfaceof a work-piece along an axis defined by gas flow from the first gassource orifice array to the surface of the work-piece while flowing asecond gas into the reactor from a second gas source orifice arrayseparate from the first gas source orifice array and disposed at asecond distance from the surface of a work-piece along the axis definedby gas flow, said second distance being less than said first distance.22. The method of claim 21, wherein the first gas comprises a reactiveprecursor.
 23. The method of claim 21, wherein the first gas comprises areactive precursor and a carrier gas.
 24. The method of claim 21,wherein the second gas comprises a reactive precursor.
 25. The method ofclaim 21, wherein the second gas comprises a reactive precursor and acarrier gas.
 26. The method of claim 22, wherein the second gascomprises a second reactive precursor.
 27. The method of claim 22,wherein the second gas comprises a second reactive precursor and acarrier gas.
 28. The method of claim 22, wherein the second gascomprises a purge gas.
 29. The method of claim 24, wherein the first gascomprises a purge gas.
 30. The method of claim 23, wherein the secondgas comprises a second reactive precursor.
 31. The method of claim 23,wherein the second gas comprises a second reactive precursor and asecond carrier gas.
 32. The method of claim 23, wherein the second gascomprises a purge gas.
 33. The method of claim 29, wherein the secondgas comprises a reactive precursor.
 34. The method of claim 29, whereinthe second gas comprises a reactive precursor and a carrier gas.
 35. Themethod of claim 29, wherein the second gas comprises the purge gas.